Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$233.36	9.837%	$256.3156	$256.32	$256.30	$256.30
Purchase #2	$28.36	12.310%	$31.8511	$31.85	$31.85	$31.90
Purchase #3	$49.87	11.127%	$55.419	$55.42	$55.40	$55.40
Purchase #4	$20.66	3.308%	$21.3434	$21.34	$21.35	$21.30
Purchase #5	$128.66	3.172%	$132.7411	$132.74	$132.75	$132.70
Purchase #6	$40.82	7.223%	$43.7684	$43.77	$43.75	$43.80
Purchase #7	$156.88	8.227%	$169.7865	$169.79	$169.80	$169.80
7 purchase totals =	$658.61		$711.2251	$711.23	$711.20	$711.20